Mantis Shrimp Holds Key to Better Composites in its Fist

by ccaldwell@fibreglast.com

The mantis shrimp is a solitary and aggressive predator of the ocean bed. In fact, it has a reputation for being a kind of “ninja of the sea,” particularly with regard to its much larger, hard-shelled prey, like clams and crabs.

It’s all because the mantis shrimp packs an impressive wallop when looking for food. The tiny front club of this four-inch creature accelerates from zero to 50 mph in just three seconds underwater with a force that equals that of a 22-caliber bullet. (That’s a pretty quick crack to an unsuspecting clam.) It’s so fast, in fact, that it creates what’s called cavitation: as the club moves, it boils the surrounding water, creating bubbles that implode and yield a secondary impact on prey. Smacks of sci-fi, doesn’t it? But seeing is believing: take a look at the killer in action.

Because the force created by the club is more than 1,000 times its own weight, researchers at the University of California, Riverside began to look at how the club of one shrimp could sustain such repeated impact (approximately 50,000 strikes) over a lifetime. Turns out, it’s a science that can be applied to composites.

“The club is stiff, yet it’s lightweight and tough, making it incredibly impact tolerant and interestingly, shock resistant,” said research leader David Kisailus. “That’s the holy grail for materials engineers.”

The Kisailus team, made up of experts in everything from zoology to mechanics, found that the club’s endocuticle region is characterized by a spiralling arrangement of mineralized fiber layers that act as a shock absorber. In a way, it forces cracks to constantly change direction, which disperses their energy and stops them from propagating.

The research team then used carbon fiber and epoxy to create composite materials based on the layered helix design of the shrimp’s club. Initial tests for impact resistance and energy absorption revealed these samples showed 20 to 50 percent less damage than samples made from unidirectional and quasi-isotropic reinforcements. Tests also revealed helix samples displayed 15 to 20 percent increase in residual strength after impact compared to other test samples.

“Biology has an incredible diversity of species, which can provide us new design cues and synthetic routes to the next generation of advanced materials for lightweight automobiles, aircraft, and other structural applications,” Kisailus said.

Kisailus recently learned he has been selected to receive a $7.5 million Department of Defense grant to continue the work of his team. You can read a comprehensive study of the nature of the microscopic structure of the mantis shrimp’s club in the journal Science.